The present invention relates to hydrocarbon mixtures obtained from petroleum cuts comprising modified polycyclic aromatic hydrocarbons or modified PACs. It also relates to methods for producing these hydrocarbon mixtures and to uses of these hydrocarbon mixtures.
The presence of aromatic compounds in hydrocarbons obtained from petroleum cuts or from their refining is a major problem for the refiner. Some aromatic compounds are necessary for the good quality of the commercial product, but others, such as polycyclic aromatic compounds or PACs, are toxic to the environment and to humans in particular. Indeed, the toxicological standards have classified some of these PAC aromatic compounds among the products exhibiting a possible carcinogenic danger.
The expression PAC is understood to mean, in the remainder of the present description, all the polycyclic aromatic compounds, including those comprising in their chemical structure heteroatoms such as sulfur, nitrogen and oxygen. Among these PACs are pure condensed PAHs or polycyclic aromatic hydrocarbons, some of which appear in the lists of products recognized as being carcinogenic and/or mutagenic products.
Accordingly, some petroleum cuts containing some of these PAHs have been classified Carcinogenic Cat2 (substances which are carcinogenic in animals).
One of the main worries of refiners is therefore to limit, or even eliminate, these PAC compounds from products sold on the market, regardless of their subsequent use.
Numerous processes have been studied for reducing the PAC content of these petroleum cuts in order to reduce their carcinogenic power.
Among these processes, many are designed to extract or convert the dibenzothiophene derivatives, the carbazole derivatives and the condensed polycyclic aromatic hydrocarbons (PAHs). The routes explored are catalytic hydrogenation, oxydesulfuration or the extraction of these compounds by formation of charge transfer complexes.
While all these processes are of interest to the refiner, the processes used are not 100% efficient on all hydrocarbon cuts and often result in a loss of materials because the undesirable products are extracted before being treated.
In the field of the treatment of bituminous sand, tar and charcoal residues, industrialists have chosen to add, to separate cuts and extracts, polymers of the group consisting of PVC, butadiene-styrene, anthracene and polystyrene oil and optionally ferric chloride, and then to heat the mixtures thus obtained so as to substantially reduce their benzopyrene content (see DE 4138561, and the publications by Janusz Zielinsky in Polymery-Tworzywa wielkoczasteczlowe, 1995, 40 (10), 591 and J. Am. Chem. Soc., Div. Fuel Chem. (1995), 40 (4), 768-770).
In patent JP 05271117, there is described the purification of aromatic naphthalene cuts extracted from coal tar containing sulfur-containing polycyclic aromatic hydrocarbons, in particular dibenzothiophenes. In this purification process, a first step consists in polymerizing, on these sulfur-containing polycyclic compounds, an olefin in the presence of an acid catalyst, clay, alumina or zeolite, preferably zeolite Y, at a temperature of between 50 and 250° C. In a second step, the polymers thus formed are then extracted by distillation, a purified aromatic cut thus being obtained.
None of the processes proposed envisages the treatment of a PAC mixture in a mixture of completely or partially aromatic hydrocarbons.
Moreover, in the polymerization field, it is known to use polycyclic aromatic hydrocarbons or PACs, taken individually, as polymerization retardants. Thus, it is possible to use individually, as retardant, naphthalene, anthracene, phenanthrene or benzopyrenes. This retardant effect essentially depends on their actual reactivity in a polymerization reaction.